The present disclosure relates to technology for non-volatile storage.
Semiconductor memory is used in various electronic devices. For example, non-volatile semiconductor memory is used in cellular telephones, digital cameras, personal digital assistants, mobile computing devices, non-mobile computing devices and other devices. Electrical Erasable Programmable Read Only Memory (EEPROM) and flash memory are among the most popular non-volatile semiconductor memories.
Some non-volatile memory cells store information in a charge storage region. Examples of charge storage regions include a conductive floating gate and a charge trapping region. As one example, a conductive floating gate is located between a conductive control gate and a channel region. Moreover, the floating gate is insulated from the conductive control gate and the channel region. As another example, a charge trapping region is located between a conductive control gate and a channel region.
A non-volatile memory cell can function as a transistor, with the threshold voltage of the transistor controlled by the amount of charge that is retained in the charge storage region. That is, the minimum amount of voltage that must be applied to the control gate before the transistor is turned on to make the channel region conductive may be controlled by the amount of charge in the charge storage region.
Data may be stored in a non-volatile memory cell by establishing its threshold voltage within a target range. Prior to programming certain non-volatile memory devices, such as a NAND flash memory device, the memory cells are erased. The erase operation removes electrons from the charge storage region, for some devices. Thus, the erase may lower the threshold voltage of the memory cell. Programming of the memory cells may be achieved by applying a program voltage to the control gate to raise the threshold voltage of the memory cell. Raising the threshold voltage occurs as a result of adding electrons to the charge storage region, for some devices.